1. Field of the Invention
The invention relates in general to devices for mining operations and in particular to a new and useful shifting device connected with a longwall conveyor for a progressive timbering frame, which consists essentially of a push rod articulatedly connected on the mining side with the longwall conveyor and of a thrust piston drive, the push rod carrying on the mining side a sliding plane control device.
2. Description of the Prior Art
Shifting devices for underground operations operate as the longwall conveyor is being shifted so that the thrust piston drive braces itself against the timbering frame clamped between the hanging wall and the foot wall and moves a conveyor against the mining face by the push rod. In addition, as the timbering frame is being shifted, the thrust piston drive pulls the timbering frame toward the longwall conveyor by the push rod. In such shifting devices, jamming of the push rod will occur again and again due to the fact that the push rod is subjected, due to the plane control device articulated to it on the mining side, to bending stresses which strive to lift or push down the gobbing side and of the push rod, depending on the direction in which the plane is articulated. These movements and stresses are caused in particular by the fact that the plane and the longwall conveyor "breathe" because of the naturally different density of the seam upon passage of the plane.
From German Application No. 25 22 117 such a shifting device has become known, in which the above-mentioned difficulties were expected to be eliminated by the fact that the gobbing side end sections of the skids of the timbering frame and of the push rod, or so-called "guide carriage", are provided in the zone of the opposite lateral faces with interengaging projections and recesses which limit the vertical mobility of the push rod. As projections there are provided here lateral pins extending essentially at right angles away from the push rod, which engage in longitudinal grooves at the opposite skid side-faces and are displaceable therein.
It was found that this design of a shifting device is not satisfactory because with it, too, jamming occurs between the guide elements on the push rod and on the skids and also at the gobbing side end of the timbering frame, caused by the fact that often only one of the two skids is lifted at the gobbing side end, either during advance of the timbering frame or because of unevennesses of the sill, so that the push rod projections engaging into the guide grooves and the push rod itself are twisted. This is especially true in the case of timbering frames with lemniscate linkages, where, upon lifting, the skids execute a vertical as well as a horizontal movement. As a result, in many cases shifting of the frame and/or the conveyor is extremely difficult and time-consuming.